This grid dataset is part of the three-dimensional (3-D) hydrostratigraphic model of the Sylvan Lake sub-basin in the Edmonton-Calgary Corridor, central Alberta. It represents the net-to-gross sandstone ratio distribution within the Paskapoo Formation - Lower Composite Slice of the Sylvan Lake sub-basin. The Lower Composite Slice is one of three distinct geological domains identified in the Paskapoo Formation of the Sylvan Lake sub-basin model. Characterization of net-to-gross sandstone ratio distribution within the Paskapoo Formation provides information about the geological heterogeneity and potential hydraulic connectivity within the formation for input into a groundwater flow model. Alberta Geological Survey (AGS) Open File Report 2014-10 includes a full description of the process used to produce the net-to-gross sandstone ratio grid.